A supercritical fluid is any substance above its critical temperature and critical pressure, exhibits properties considerably different from a fluid under a normal condition, and distinctive phenomena may be seen in its reaction characteristics also when used as a reaction area. Decomposing organic substances such as fluorocarbon gas, dioxin, and PCB (compound of polychlorobiphenyl) by using water of near-critical or supercritical condition is disclosed in Japanese Patent Application (Kokai) No. 2001-149767.
As the supercritical fluid, for example, when water is used to form a supercritical fluid, water becomes supercritical water when it exceeds high temperature and high pressure condition of a temperature at 374° C. and pressure at 22 MPa. Such supercritical water possesses properties of both vapor and water, and is capable of dissolving organic substances. Recently, research and development to oxidize and decompose substances such as PCB and dioxin in supercritical water is being conducted to make use of such properties.
A significant condition when conducting such reaction is temperature and pressure.
In many cases, by changing the condition of the temperature, it is possible to cause different reactions to the reactant.
Further, even in hot water of near-critical condition not reaching the supercritical condition, it is possible to cause a distinct reaction dependent on that temperature and pressure condition.
Note that in the present specification, the meaning of the term “hot water” other than supercritical water, also includes water capable of causing a distinct reaction dependent on temperature and pressure condition such as those of the above near-critical condition.
Further, it is possible to cause a different reaction by adding some type of additive into the water or to the reactant. Note that “different reaction” herein in addition to mainly meaning a reaction producing different products of reaction, in a broad sense, it also means a reaction of different reaction speed and a reaction of different yield of the reaction product even when producing the same reaction product.
When treating mass reactants, the so-called continuous type apparatus is often used. Normally, the reactant is transformed into a slurry by a pre-process, and the reactant together with water are successively fed into the apparatus to be highly pressurized, gradually heated by a heater around a pipe, reaction occurs when heated to the target temperature, and then successively discharged from the apparatus after cooling.
In an apparatus such as the above one, because the reactants are gradually heated, before reaching the target temperature condition, the passing of the reactants through a temperature that is lower than the target temperature cannot be avoided and therefore a reaction not aimed at may occur in the low temperature condition.
As an apparatus capable of preventing a reactant from a temperature condition that is not the target temperature, or introducing the reactant into hot water for just an instant even if it is not the target temperature, a rapid injection type reactor illustrated in FIG. 8 is known. This reactor is mainly applied to reactants R that are solids to a certain degree.
The reactor illustrated in FIG. 8, as a supply system of hot water, it comprises a tank 11 that stores normal temperature and normal pressure water W for use, a pump 12 that delivers the water W from the tank 11 and raises the pressure until the target high pressure, a heater 13a disposed in the periphery of a pipe to heat the high pressure water W′ inside the pipe, and a pre-heater 13 provided with a temperature sensor 13b for measuring the temperature of the heater 13a. 
As a supply system of the reactant R, it comprises a standby chamber 23 for temporarily holding the reactant R, a valve 24, and a pipe 25.
As a reaction system of the reactant R, it comprises a reacting vessel 31 for performing a predetermined reaction treatment to the reactant R, a heater 32 disposed in the periphery of the reacting vessel 31 to heat the reacting vessel 31 to a predetermined temperature, a temperature sensor 33 for measuring the temperature inside the reacting vessel 31, and a pressure sensor 34 for measuring the pressure inside the reacting vessel 31.
As an exhaust system, it comprises a pipe 41 connected to the bottom of the reacting vessel 31 and a cooler 42 configured so that coolant supplied from an unillustrated coolant circulatory device circulates to the periphery of the pipe 41, and cools the hot water HW to about room temperature.
In the above reactor, all the pipes including the pipes 25 and 41, the standby chamber 23, and the reacting vessel 31 are filled with water.
Further, each of the pipes and the reacting vessel 31 are formed of a material having a quality that can withstand high temperature and high pressure, such as SUS316, Inconel or Hastelloy.
A reaction treatment of a reactant R by the above reactor will be explained.
First, the normal temperature and normal pressure water W extracted from the tank 11 is pressurized at the pump 12 to thereby become a high pressure water W′ of high pressure and the high pressure water W′ is continuously fed to the pre-heater 13. The high pressure water W′ in the pipe is heated by the pre-heater 13 to a predetermined temperature where it becomes hot water HW and fed into the reacting vessel 31 and discharged from the reacting vessel 31 to the pipe 41. The hot water is cooled to a temperature of about room temperature by the cooler 42 and discharged to the outside of the apparatus.
Here the inside of the reacting vessel 31 is heated to a predetermined temperature by the heater 32.
Under the above states the reactant R held in the standby chamber 23 falls into the reacting vessel 31 via the pipe 25 by opening the valve 24, and reaction treatment such as oxidative decomposition is performed on the reactant R by the hot water HW in the reacting vessel 31. The reaction product and a reactant R not reacted are discharged with the hot water HW via the pipe 41 and after being cooled by the cooler 42 to a temperature of about room temperature, they are discharged to the outside of the apparatus.
Here, since the reactant R temporarily remains in the standby chamber 23, the standby chamber 23 needs to be made about room temperature.
To maintain the temperature from the valve 24 to the upper portion close to room temperature, the pipe 25 must have the function to cut off the high temperature at the reacting vessel 31 in addition to having the function of letting the reactant R pass through. Therefore, making the pipe 25 to a certain length so that it may cool off naturally is conceivable.
However, if the pipe 25 is made long, it will take time for the reactant R to fall and during that time the reactant R will be subjected to hot water of a temperature lower than the target reaction temperature, and thus is not preferable.
Therefore, without making the pipe 25 too long, but instead it is conceivable to provide an unillustrated fin for air cooling around the pipe 25 and to circulate an unillustrated coolant. The length of the pipe 25 and an unillustrated cooling mechanism thereof were designed taking into consideration these thermal conduction.
On the other hand, the reactant R introduced into the reacting vessel 31 decomposes and diffuses, and a portion thereof reaches the pipe 25 also. That is, when a pipe of the above length and the unillustrated cooling mechanism thereof are designed, the reactant R will also be exposed to a temperature that is considerably lower than the target temperature.
Because the cooling mechanism is designed so that the temperature nearby the valve 24 side of the pipe 25 is considerably lower than the temperature of the reacting vessel 31, the temperature will be close to room temperature.
This is, from the aim of the apparatus, although not quite preferable, it is deemed that the influences thereof are of a level that can be ignored.
However, the temperature of the valve 24 and that of the standby chamber became a temperature considerably exceeding a design expectation value when the apparatus was actually put in operation. The reason for this resides in the occurrence of a convection current of the water in the pipe 25 which was not assumed.
This situation is shown with reference to FIG. 9. The high temperature and high pressure water HW inside the reacting vessel maintained at that temperature had reached the valve 24 or near the valve 24.
That is, the temperature of the hot water HW inside the reacting vessel is higher than that of the water in the pipe 25, so the density of this part of the hot water HW becomes smaller due to swelling and rises due to buoyancy, and the water inside the pipe 25 flows into the reacting vessel in place of this hot water HW to generate a circulating flow in the pipe 25.
Due to this convection flow, the valve 24 is overheat, thus a problem of receiving thermal damages occurred. Presently, there is not valve usable under the above high temperature and high pressure condition, and therefore to prevent damages to the valve, a method of strengthening the cooling at the pipe 25 is conceivable, however, there is a limit to air cooling, etc., so the length of the pipe 25 is made extremely long to cope with this problem.
As described above, the reactant R passing through the pipe 25 needs a more longer time, and this is not preferable from the aim of the apparatus. That is, exposing the reactant R to a temperature that is lower than the target temperature and damages to the apparatus is a trade-off.
Further, the convection current at the pipe 25 also carries the reactant R which has dispersed (dissolved) in the water introduced into the reacting vessel to the upper portion of the pipe 25. That is to say, the reactant R is exposed to a temperature that is considerably lower than a target reaction temperature.
This becomes a major problem compared with the above problem caused by diffusion and the problem caused by the time subjecting the reactant R to a temperature that is not the target temperature at the pipe 25 when the reactant R is fed thereto.
As explained above, the conventional apparatus illustrated in FIG. 8 is not capable of making the reactant R react at a target temperature.